PORTLAND, Ore. – The Portland Water Bureau lifted the most extensive boil water notice in its history Saturday morning after dozens of new water samples tested negative for E. coli bacteria.

The bureau said on its website that tap water is safe to drink, however it recommends flushing all taps for 2 minutes or until the water runs cold before drinking tap water for the first time. Doing so will flush any water that might be contaminated.

"The risk is really, really, really small," said David Shaff, the water bureau's administrator. "It's almost immeasurable."

State health officials detected E. coli bacteria in water samples at three locations over a three-day period earlier this week, which Shaff called a "highly unusual event."

Shaff says the 24-hour boil notice was issued in cooperation with the Oregon Health Authority out of an abundance of caution.Scientists detect E. coli, which indicates animal waste, in Portland's water supply about once every two months.

In those cases, however, they only find the bacteria in one place and don't feel it's necessary to warn the public while still reporting the results to other authorities, according to Shaff.